Epidemiologic studies are conducted to identify life-style and environmental risk factors for cancer and to investigate their interrelationships with genetic determinants of these diseases. Case-control studies of cancers of the bladder, prostate, pancreas, esophagus, stomach, lung, brain, and head and neck, as well as non-Hodgkins lymphoma and multiple myeloma, are in progress. A large case-control study of bladder cancer is progressing in Spain to identify occupational bladder carcinogens and to evaluate non-occupational exposures including cigarette smoking (black vs. blond tobacco), phenacetin-containing analgesics, dietary factors, and urination frequency and pH. As expected, smoking was found to be a powerful risk factor for bladder cancer and suggested an increased risk associated with environmental tobacco smoke among nonsmokers of cigarettes. This study quantified, for the first time, that the large male excess of bladder cancer in southern Europe may be almost entirely due to smoking. In contrast, regular use of nonsteroidal anti-inflammatory agents were associated with a reduced bladder cancer risk in Spain. No increased risk of bladder cancer was assoicated with overall use of hairdyes or use of permanent hair dyes and no trend in risk with increasing exposure was seen for duration of use, average use or cumulative use. In contrast, a case-control study of brain cancer in Nebraska suggested that women who used hair dyes had a significant two-fold risk of glioma, particularly among long-term users and those who used permanent hair dyes. A large case-control study of bladder cancer in New England is underway to determine the reasons for the persistently elevated bladder cancer mortality and incidence in the northeastern United States. Genetic susceptibility markers also will be evaluated in relation to bladder cancer risk, as well as their interaction with epidemiologic risk factors. Studies of participants in a large screening trial for prostate, lung, colorectal, and ovarian cancer (PLCO Trial) examined meat and meat cooking methods in relation to risk of both prostate cancer and colorectal adenomas. Use of hormone replacement therapy and reproductive history were also examined in relation to colorectal adenomas in the PLCO Trial. In Shanghai, preliminary results of analysis of a large cohort of women indicate that risk of breast cancer was elevated among those exposed to environmental tobacco smoke.